Motor vehicle drive trains generally include a substantially tubular drive shaft and one or more axles driven through a differential mechanism. Collectively, this drive chain is driven by a prime mover, such as an engine, through a transmission. Drive shafts, sometimes referred to as propeller shafts, are remarkably simple mechanically but are a vital element of the drive train. It has long been recognized that balancing of the drive shaft is a key element in improving the overall performance of the drive train. A well-balanced drive shaft results in a motor vehicle which is smoother and quieter. In addition, reducing or removing excessive vibration in the drive shaft contributes to increased component life of the remaining components in both the drive shaft and motor vehicle.
A wide variety of methodologies have been developed for the automated testing and balancing of tubular drive shaft elements. Modern computers, by virtue of their low cost and versatility, have become commonplace components in the process of drive shaft balancing. Utilizing testing equipment which is capable of determining the precise angular position of a drive shaft in relation to a test fixture, it is possible to analyze the vibrational signature of a drive shaft with exquisite precision. The information generated by such computers can then be fed back to an operator or automated machine to assist in the precise location of counterweights in relation to the drive shaft, thereby minimizing its tendency to vibrate over a wide range of speeds and operating conditions.
The existing methodologies all generally involve placement of a drive shaft or similar rotating element in a fixture similar to an ordinary lathe. The drive shaft is suspended from spindles on opposing ends of the machine, and rotated rapidly on the spindles utilizing well known power means. Sensors associated with the spindles determine an out-of-balance condition and provide a computer display or printout of the angular position on the shaft corresponding to an imbalance. Modern computers in this application are also programmed to identify the amount of counterweight required in order to bring the shaft into balance. In other words, both the position of the imbalance and the mass and location of the necessary counterweight are provided by the associated computer.
In the current state of the art, individual weights of varying sizes and masses are attached to the shaft by projection welding. Such weights have small “feet” or projections which facilitate the attachment of the weight to the outer surface of the shaft. The weights themselves are generally small rectangular elements having a curvature which matches or approximates the curvature of the outer circumference of the shaft. In the current state of the art, an operator either manually positions or instructs a robotic element to position the necessary weight on the propeller or drive shaft in an appropriate position in relation to the out-of-balance position. The required weights are then secured to the propeller shaft by an automated welding device. This process may require the positioning of one or more weights of varying sizes in different angular positions on the circumference of the shaft. Once the welding operations are completed, the shaft is again tested to verify that the weight positioning is correct.
In the current state of the art, the task is work-intensive, requiring the operator to frequently stop and start the balancer, determine the proper location for the weights, locate suitable size and mass of weight, manually position the weights on the shaft, operate the welding apparatus for securing the weights to the shaft and then verify the positioning. Numerous efforts have been made over the years to automate this process. However, one of the principal impediments to automation has been the necessity to select from an inventory of several dozen different sizes and masses of balancing weights.
One unsuccessful effort has been made to utilize a continuous strip of metal ribbon as a source for automated fabrication of the necessary weights. In this method, a coil of steel is mounted to a spool and positioned adjacent to the balancing apparatus. When the balancing apparatus has determined the necessary position and mass for the weight, under computer control, an appropriate segment of the coil of steel is cut and fed to the balancing apparatus for robotic placement on the propeller shaft and subsequent welding. This method has been discarded inasmuch as it requires the storage, movement and manipulation of a coil of steel, which tends to be inordinately heavy and bulky. The process of cutting the required segment of steel with precision has also been fraught with difficulties. For these and other reasons, the “cut on site” methodology has not been widely accepted in the industry.
It would be desirable to provide an automated method for balancing a drive shaft.